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Re: SSL Certificates per domain

... Could this be a case where it makes sense to run multiple instances of postfix which bind to different IP s and are each configured with unique certs? kind

Message 1 of 8
, Jun 1, 2010

On 06/01/2010 10:00 AM, Victor Duchovni wrote:

> On Tue, Jun 01, 2010 at 10:20:56AM -0400, Wietse Venema wrote:
>
>>> Common Name: myserver.domain.com
>>> MX for domain1: smtp.domain1.com
>>> MX for domain2: smtp.domain2.com
>>>
>>> Then, how i configure SSL Certificates per domain on Postfix?
>>> References?
>>
>> How would Postfix know what certificate to use?
>> Hint: SMTP is not HTTP.
>
> Now that OpenSSL 1.0 is out, and has "always on" support for TLSv1
> extensions, I may find some time to add SNI support to Postfix. This
> creates significant additional complexity in the SMTP server SSL
> state management, and with most users on 0.9.8 or even 0.9.7, it
> has not yet been a priority.
>
> Even with SNI support, most SMTP clients will not make use of SNI, so
> it will take a long time before SMTP STARTTLS servers can expect to
> support multiple certificates for most clients.
>

Could this be a case where it makes sense to run multiple instances of postfix which bind to different IP's and are each
configured with unique certs?

> > Even with SNI support, most SMTP clients will not make use of SNI, so
> > it will take a long time before SMTP STARTTLS servers can expect to
> > support multiple certificates for most clients.
> >
>
> Could this be a case where it makes sense to run multiple instances
> of postfix which bind to different IP's and are each
> configured with unique certs?

Yes, clearly, that's the most practical configuration option today.

--
Viktor.

/dev/rob0

... They don t need to be separate instances, possibly just separate smtpd(8) listeners bound per IP address. If you want each smtpd s input to be a separate

Message 3 of 8
, Jun 1, 2010

On Tue, Jun 01, 2010 at 12:23:38PM -0500, Terry Inzauro wrote:

> Could this be a case where it makes sense to run multiple
> instances of postfix which bind to different IP's and are each
> configured with unique certs?

They don't need to be separate instances, possibly just separate
smtpd(8) listeners bound per IP address. If you want each smtpd's
input to be a separate output stream, that would either require
separate Postfix instances, or the new features in Postfix 2.7
(release notes and the list archives have more information.)

Is SNI defined for SMTP yet? A quick Google search didn't find it.
How would that work? The client would have to tell the hostname or
domain name wanted before the STARTTLS?
--
Offlist mail to this address is discarded unless
"/dev/rob0" or "not-spam" is in Subject: header

Victor Duchovni

... SNI works entirely within SSL, the desired hostname is sent in the client SSL HELLO. There is no need to define SNI for SMTP. An MUA that implements SNI

Message 4 of 8
, Jun 1, 2010

On Tue, Jun 01, 2010 at 12:42:06PM -0500, /dev/rob0 wrote:

> Is SNI defined for SMTP yet? A quick Google search didn't find it.
> How would that work? The client would have to tell the hostname or
> domain name wanted before the STARTTLS?

SNI works entirely within SSL, the desired hostname is sent in the
client SSL HELLO. There is no need to define SNI for SMTP.

An MUA that implements SNI for submission, would send the SMTP server
name it expects to match. This case is easy.

An MTA delivering mail to an MX host faces a more complex choice,
because it may be willing to accept a variety of names. The best
choice would be to send the "nexthop" domain (typically the same
as the domain of the recipients), and the server will choose a
cert with that name if it has one, a cert for a sub-domain
otherwise, and the default cert if neither an exact match, nor
a sub-domain are available.

On the client side, we may need to a new policy table attribute to
allow the client administrator to specify an SNI name other than the
nexthop.

Anyway, this is not currently a high priority, if implemented, it would
largely be just Postfix talking to Postfix. I am not aware of any other
SMTP+STARTTLS implementations that support SNI.

--
Viktor.

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